Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother. (Matthew 18:15)

Today’s big question: what if a fellow Christian refuses to repent?

Thankfully, the Bible is quite clear about what to do when a Christian sins against you and refuses to repent. But if your brother or sister in Christ is not repenting, you first need to take a look at someone else—yourself. First, you need to double-check your motives for confronting someone. Make sure there aren’t any planks in your own eye (Matthew 7:1–5).

Second, verify that what the person did was indeed a sin as defined by God’s Word. Borrowing your lawn mower and not giving it back right away doesn’t count. Once you’ve examined yourself, verified that your fellow Christian did indeed sin, lovingly confronted the individual, and yet still receive resistance, it is time to involve other witnesses and eventually church leadership.

Jesus gave us step-by-step instructions:

But if he will not hear, take with you one or two more, that “by the mouth of two or three witnesses every word may be established.” (Matthew 18:16)

Jesus quoted Deuteronomy 19:15 which teaches that in order for an accusation of a crime (or sin) to be considered true, a testimony of two or more witnesses was required. So if a personal appeal fails, take a fellow witness (or witnesses) to confront the professing Christian. If the person is truly guilty and remains unrepentant, proceed to the next step Christ gave:

And if he refuses to hear them, tell it to the church. But if he refuses even to hear the church, let him be to you like a heathen and a tax collector. (Matthew 18:17)

This does not mean you get up to announce the sin in front of everyone during service or talk about it with your Bible study group. Rather, go to the leadership of your church. They will then be responsible to confront this person. However, if that person is still unrepentant, then the leadership must make the difficult decision of removing the individual from the fellowship of the church.

Assuredly, I say to you, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven. (Matthew 18:18)

Here Jesus assures the future leaders of His church that they are given the authority to make such difficult decisions. This binding and loosing is not at the mere whim of the leadership but is associated with the reverent and obedient following of God’s plan for discipline. This discipline was instituted by God, but He uses His church to enact and enforce it. The ultimate goal in this process is to restore the person to a right standing with Christ and His church (Galatians 6:1). http://www.answersingenesis.org/articles/2011/01/28/fellow-christian-refuses-to-repent